What is the ruling on the water separated from washing impurity before the place itself is purified?
Chapter on Praying with Impurity and Other Matters
Al-Mughni
Book of Prayer
Primary text
Water separated from washing impurity before the place becomes pure is divided into three categories. First, if it separates changed by the impurity, it is impure by consensus, as it is water affected by impurity. Second, if it separates unchanged before the place is purified, it is also impure because it is a small amount of water that contacted an impurity it did not cleanse, thus becoming impure, similar to the changed water or the residue remaining in the place. Third, if it separates unchanged from the washing that purified the place, the soundest opinion is that it is pure, as held by Al-Shafi'i. This is because it is a part of the attached water, which is pure, and it is water that removed the legal effect of the impurity without being changed by it.
Supporting text
A second opinion, held by Abu Hanifa, is that this third type of water is impure because it is a small amount of water that contacted an impurity and thus became impure, similar to water that flows over it. If judged as pure, there are two views on whether it retains its purifying quality: one view states it is purifying because its original state is purification and what happened did not contaminate or change it; the second view states it is not purifying because it removed an impediment to prayer, akin to something that lifts ritual major impurity (Hadath).